Functional lake connectivity in the Colville Delta, Alaska: spatiotemporal patterns, drivers, and impacts on ice phenology

Arctic deltaic floodplains consist of complex river and lake systems that respectively transport and store both inorganic and organic materials. The connectivity of Arctic floodplain lakes to nearby channels determines how much river water these lakes receive each year. This interaction, in turn, influences carbon storage and ecological productivity and diversity. Prior research has used in situ and remotely sensed data to identify lake connectivity status at single instances in time. As the Arctic hydrologic cycle responds to climate change, it is important to understand how connectivity, and connectivity-dependent processes, will be impacted. Here we present an algorithm, applied to 91 lakes in the Colville River Delta, Alaska, which uses Landsat-derived water color observations to assess summertime functional lake connectivity within five-year intervals between 2000 and 2019. Comparison of results for 72 lakes against manual classification of lakes from high resolution imagery shows that our method correctly identifies functional connectivity with an overall accuracy of 0.92 and a kappa statistic of 0.84. We find that elevated maximum summer discharge corresponds to increased functional connectivity within the delta. Additionally, results show that functional connectivity is highly correlated to lake ice phenology. Climatologically, spring ice breakup begins an average of 26 days earlier in high functional connectivity lakes compared to low functional connectivity lakes, and breakup ends approximately 19 days earlier. Within these lakes, increased open water during the high-sunlight early summer period may allow for increased photochemical activity. The algorithm presented here can be applied to other high-sediment and lake-rich Arctic deltas to better understand both the spatial and temporal variability of connectivity, as well as the impact that these variations have on deltaic carbon cycling and ecology.